The present invention relates to a method and a device for contactless measuring of a strand-like textile material of indeterminate extended length, and more particularly to such a method and device basically operative by irradiating the textile material within a measuring range of at least one ray source, imaging the textile material on a sensor range of a receiving device comprising sensor cells, and converting the signals produced by the individual sensor cells into measured values for the dimensions of the textile material.
In the case of strand-like material such as, e.g., yarns, etc., properties must be continuously measured or monitored in a series of production or processing steps. In particular, properties such as the diameter of the particular material to be measured and its variations require measurements with a high degree of precision.
In order to determine the diameter, Swiss Patent CH 643,060 teaches illuminating a strand-like body by a light source and receiving the illumination state thereby produced by means of an image sensor wherein its photosensors are individually scanned and the local illumination state determined by each photosensor is examined to determine whether it reaches or exceeds a given threshold value. The signals of the photosensors must reach or exceed this threshold value if they are to be considered as a contribution to the total measured value and transformed in an evaluation device into measured values for the diameter of the body. If the signal of a photosensor reaches or exceeds the threshold value the photosensor is evaluated as illuminated. If the signal does not reach the threshold value the photosensor is evaluated as not illuminated. The reference contemplates possible use in yarn cleaners.
A yarn Nm 40 has a diameter of approximately 250 .mu.m. Suitable and customary image sensors for determining the diameter of such a yarn have a resolution of 10 to 30 .mu.m. The image resolver described in Swiss Patent CH 643,060 is, e.g., a CCD line sensor which contains 500 photoreceivers or sensor cells in a width of 7.5 mm and thus has a resolution of 15 .mu.m resulting from the interval and the width of the photoreceiver. Thus, an error of .+-.6% can occur, conditioned by the method described in it, when determining the diameter, and in other image sensors cited above up to a range of .+-.10%. However, a measured value with an error of less than 1% is required for yarn cleaning.